1. Technical Field
The present invention relates generally to an ignition apparatus or coil, and, more particularly, to a twin spark pencil coil with provisions to balance load capacitance.
2. Discussion of the Background Art
An ignition apparatus for producing a spark for ignition of an internal combustion engine has been developed in a variety of different configurations suited for the particular application desired. For example, it is known to provide an ignition apparatus that utilizes a secondary winding wound in a progressive winding pattern, specifically for “pencil” coil applications. A pencil coil is one having a relatively slender configuration adapted for mounting directly to a spark plug in a spark plug well of an internal combustion engine. A feature of a “pencil” coil is that a substantial portion of the transformer (i.e., a central core and primary and secondary windings) is located within the spark plug well itself, thereby improving space utilization in an engine compartment. In one configuration, an outer core or shield is allowed to electrically float, as seen by reference to U.S. Pat. No. 6,463,918 issued to Moga et al. entitled “IGNITION APPARATUS HAVING AN ELECTRICALLY FLOATING SHIELD.”
It is also known to provide an ignition apparatus that provides a pair of high voltage outputs suitable for generating a spark to a pair of different spark plugs. In such a known product, however, the transformer portion is not mounted within the spark plug well like a pencil coil, but rather is mounted outside of and above the spark plug well and has been referred to as a plug top coil. The known plug top ignition coil employs one long boot to mate to the spark plug and includes a second tower that provides a high voltage suitable for generating a spark to another spark plug. The high voltage produced on the second tower may go to a mated cylinder undergoing an exhaust stroke (i.e., at the same time as the principal cylinder is undergoing a compression stroke—a so-called “waste” spark ignition system). Alternatively, the high voltage on the second tower may go to a second spark plug in the same cylinder. The latter arrangement may employ a center-tapped secondary winding, with a first portion of the secondary winding being wound in an opposite direction relative to a second, remaining portion of a secondary winding. This opposite winding orientation coupled with a center tap going to ground provides two negative sparks to two spark plugs which may be installed in the same cylinder. A problem with the plug top ignition coil for twin spark operation however, relates packaging. Specifically, a relatively large area above one of the two spark plug wells is needed in order to mount the plug top ignition coil. In addition, an extra bracket may be needed, which can increase cost and complexity.
It is also known to provide an ignition system providing spark for two ignition plugs in each cylinder from a single ignition coil, as seen by reference to U.S. Pat. No. 4,177,782 issued to Yoshinari et al. While Yoshinari et al. disclose an impedance circuit element, it is provided to disturb a balance of the output voltages from the secondary coil terminals.
There is therefore a need for an ignition apparatus or coil that minimizes or eliminates one or more of the problems as set forth above.